Multiple Radio Access Technologies (RAT) are being commonly deployed in the same geographical areas by the same or different operators. There are also already several frequency bands standardized for multiple technologies. For instance according to various Third Generation Partnership Project (3GPP) standards different types of technologies such as Global System for Mobile Telecommunications (GSM), UMTS Terrestrial Radio Access Network (UTRAN), Evolved UTRAN (E-UTRAN) etc. may operate in the same frequency band. There are even bands in which both 3GPP and non-3GPP technologies such as Code Division Multiple Access 2000 (CDMA2000) or High Rate Packet Data (HRPD) can be deployed. Secondly the multifarious technologies may also co-exist in adjacent carrier frequencies in the same band. The radio transmission and reception requirements, which are specified in the standard, are generally different for different types of technologies. E-UTRA supports multiple bandwidths ranging from 1.4 MHz to 20 MHz. Thus the out of band emission requirements of E-UTRAN are adapted to support larger bandwidths. E-UTRAN may sometimes also be referred to as Long Term Evolution (LTE).
According to the E-UTRAN standard, a resource block size is 180 KHz comprising 12 sub-carriers each with 15 KHz carrier spacing and 0.5 ms time slot in frequency and time domains, respectively. The Transmission Time Interval (TTI) comprises 2 time slots, which correspond to 1 ms length in time. The radio frame is 10 ms long.
The E-UTRA uplink uses Single-Carrier Frequency Division Multiple Access (SC-FDMA) whereas the downlink uses Orthogonal Frequency Division Multiple Access (OFDMA). The SC-FDMA can be regarded as a special form of OFDMA. More specifically it is a linearly pre-coded OFDMA scheme resulting in lower Peak to Average Power Ratio (PAPR). The lower PAPR implies relatively smaller User Equipment (UE) power back-off, or maximum power reduction, to meet the emission requirements. Due to these reasons the SC-FDMA is considered more suitable for uplink transmission. Both OFDMA and SC-FDMA or any variant of OFDMA ensures inter-user orthogonality.
Thus by the virtue of SC-FDMA in the E-UTRA uplink which allows the possibility of frequency domain scheduling, the users' transmissions within the same cell are orthogonal. This means an E-UTRA terminal can transmit with relatively higher power without interfering with other E-UTRA terminals in the uplink. Due to higher terminal transmission power, the radio emissions emanating from E-UTRAN have more severe impact on the performance of the co-existing victim GSM or UTRAN radio networks rather than the other way around.
Although a wireless device typically operates in a well defined portion of the frequency band, emissions outside its operating bandwidth and also outside its operating band are unavoidable. Therefore, terminals as well as base stations have to fulfil a specified set of Out Of Band (OOB) emission requirements. The objective of OOB emission requirements is to limit the interference caused by the transmitters, terminals or base stations, outside their respective operating bandwidths to the adjacent carriers or bands. In fact, all wireless communication standards such as e.g. GSM, UTRAN, E-UTRAN, Wireless Local Area Network (WLAN) etc, clearly specify the OOB emission requirements to limit or at least minimize the unwanted emissions. They are primarily approved and set by the national and international regulatory bodies e.g. ITU-R, FCC, ARIB, ETSI etc.
The major OOB emission requirements, which are typically specified by the standards bodies and eventually enforced by the regulators in different countries and regions for both terminals and base stations comprises: Adjacent Channel Leakage Ratio (ACLR), Spectrum Emission Mask (SEM), Spurious emissions and/or In-band unwanted emissions.
The specific definition and the specified level of these requirements can vary from one system to another. Typically these requirements ensure that the emission levels outside an operating bandwidth or band in some cases remain several tens of dB below compared to the wanted signal in the operating bandwidth. Although OOB emission level tends to decay further away from an operating band, they are not completely eliminated in at least the adjacent carrier frequencies. Just to mention some arbitrary examples, In E-UTRAN the terminal ACLR is 30 dB for an adjacent E-UTRA carrier. However, E-UTRA terminal ACLR for an adjacent UTRA carrier is 3 dB tighter i.e. 33 dB. In UTRA FDD (WCDMA) the terminal ACLR is 33 dB
The frequency bands, channel arrangements and radio requirements applicable for the GSM operation are standardized. Also the frequency bands for UTRAN FDD (WCDMA) operation are standardized. The same set of specifications provides a complete set of UTRAN FDD minimum radio requirements including those related to the Out Of Band emissions for mobile terminal and the base station. These requirements are used by the manufacturers to build products such as e.g. mobile terminal and base station.
Similarly the frequency bands and channel arrangements applicable for E-UTRAN operation are standardized. The same set of specifications also provide a complete set of E-UTRAN (FDD and TDD) minimum radio requirements including those related to the out of band emissions for mobile terminals and base stations. These requirements are used by the manufacturers to build E-UTRA products such as e.g. mobile terminal and base station.
One observation about the bands standardized for GSM, UTRA and E-UTRA is that a large number of these bands are applicable for all the three technologies, i.e. GSM, UTRA and E-UTRA, whereas few of them are exclusively for one or two of these access technologies. Nonetheless, a large number of bands are specified to be applicable for all the technologies. For instance GSM band I (450 MHz) is not used for UTRAN or E-UTRAN.
Even if a band is common for multiple technologies, the channel arrangement and radio requirements for each individual technology are specified in its respective set of specifications.
For instance the following three frequency bands are commonly applicable for GSM, UTRAN FDD and E-UTRAN FDD: GSM bands: extended 800 (band V), 1800 (band VII) and 1900 (band VIII); UTRAN FDD bands: VIII, III and II and E-UTRAN FDD bands: 8, 3 and 2.
Similarly frequency bands 2 GHz and 2.6 GHz are specified for both UTRAN FDD and E-UTRAN FDD: UTRAN FDD bands: band I: 2 GHz and band VII: 2.6 GHz; E-UTRAN FDD bands: band 1: 2 GHz and band 7: 2.6 GHz.
Evidently from the above examples it is inferred that the operation of multiple technologies within the same band in the same region would be inevitable. Indeed common frequency bands such as 800 MHz, 1800 MHz, 2 GHz and 2.6 GHz are considered to be interesting candidates for the operation of more than one technology.
Furthermore, when more than one technology is used in the same band then their operation in the adjacent carriers would also be a frequent case. Since the most severe impact of the Out Of Band emission is in the adjacent or the closest carriers, therefore ACLR requirements may be stringent enough to ensure sufficient protection. As previously discussed above, and depending on terminal output power distribution, the out of band emissions and particularly the adjacent channel interference are unavoidable. This in turn leads to performance degradation and overall capacity loss.
It may be noted that the UTRAN FDD operation adjacent to an operating E-UTRA carrier is particularly vulnerable to the emissions caused by the E-UTRA carrier. This is because the E-UTRA terminal power distribution is higher compared to that of the UTRA terminal. This in turns leads to higher out of band emissions from E-UTRA towards UTRA FDD causing higher degradation in UTRA performance. The higher terminal power distribution causes degradation on adjacent systems and can either be handled by more stringent out of band emission requirements, which are not feasible from the terminal implementation point of view. Alternatively this can be addressed more conveniently by controlling the terminal transmission power by means of a suitable power control scheme.
In E-UTRAN the uplink power control has both open loop component and closed loop components. The former is derived by the mobile terminal in every sub-frame based on the network signalled parameters and estimated path loss or path gain. The latter part is governed primarily by the Transmit Power Control (TPC) commands sent in each sub-frame, i.e. active sub-frame where transmission takes place, to the mobile terminal by the network. This means the mobile terminal transmits its power based on both open loop estimation and TPC commands.
Furthermore, using the principles of power control open and closed loop components as described above, the mobile terminal sets the uplink transmit power for PUCCH or PUSCH or Sounding Reference Signals (SRS) channels depending upon which of these channels (PUCCH, PUSCH and SRS) are transmitted in a sub-frame.
The uplink transmitted power for RACH transmission is only based on the open loop components such as i.e. path loss and network signalled parameters.
The network can also estimate both open loop components, including path loss, and closed loop components of the uplink transmitted power since parameters and TPC commands are transmitted by itself. The network is also aware of the total number of active users in a cell. In this way the network may infer the total amount of interference experienced in the uplink due to uplink transmission. This allows the network to set various set of signalled parameters and monitor the consequence of power control on the uplink interference.
Thus the uplink power control in E-UTRAN is governed by a number of network controlled parameters. Therefore, in E-UTRAN, the uplink power control is highly parameterized. The mobile terminal derives its transmitted power for uplink transmission in each sub-frame using the configured parameters in conjunction with the received TPC command and the estimated path loss. This result in that the mobile terminal uplink transmitted power in E-UTRAN is highly sensitive to the parameters set by the network. Furthermore, there is also a possibility to configure a mobile terminal to accumulate certain number of consecutive power control commands. This may cause large change in the transmitted power of the mobile terminal in one direction in case it receives several consecutive up or down commands. Furthermore, due to the packet oriented nature of E-UTRAN, the change in power in one sub-frame can be very large e.g. 10-20 dB. In summary all these factors contribute to relatively higher terminal output power in E-UTRAN. Unnecessarily high terminal output power would not only increase uplink received interference within an operating carrier frequency but also adversely impact the reception quality at the adjacent carriers. The uplink in E-UTRA is orthogonal i.e. inter-E-UTRA user orthogonality in the same cell, which mean that high terminal transmit power may not have negative impact on other E-UTRA users.
Furthermore, as multiple technologies may co-exist in the same band, a multi-RAT adjacent channel scenario as described herein may occur occasionally.
Hence, highly parameterized E-UTRA uplink power control makes non E-UTRA carrier operation in adjacent carriers highly vulnerable to interference. Thus inappropriately chosen uplink power control parameters would lead to significant loss in the UTRAN capacity when operating in an adjacent carrier. Currently, there is no restriction on the ranges of parameter employed for the E-UTRA terminal uplink power control.
It may be mentioned as an illustrative example that the UTRAN FDD capacity loss when E-UTRAN/LTE is an aggressor may be in the order of 25%, according to some estimations.